Single-element modified impedance relay



Feb. 20, 1951 s. GOLDSBOROUGH SINGLE-ELEMENT MODIFIED IMPEDANCE RELAY Filed March 24, 1948 ML H INVENTOR 6y L. Go'ldsboraugh ATTORNEY Patented Feb. 20, 1951 SINGLE-ELEMENT MODIFIED IMPEDANCE Y RELAY Shirley L Goidsbor ugh sk ng .Rid c N. J a sign r to Wes in house Ele tri Corporation, East Pittsburgh, a, a p ation o Pennsyania Application Marsh :2 'i.'l N: 1 ,572

Z'Clairns. I 1

My invention relates to a single element modified impedance relay which is associated with networks fer making the proper phase-selection for responding to a phase-to-phase fault on a threephase line which is being protected.

My Patents 2,393,983 and 2,404,955, both issued in 1946, show modified-impedance distance-measuring phase-fault detectors, with triple adjustments for adjusting the size and position of .the response-circle which shows the relay-eharacteristic when the baIance DQints of the relay are plotted on rectangular coordinate in terms of the line-resistance and the line-reactanee. Thi relay-characteristic is a circle having its center displaced from the orig-in, and lying in a line at an angle which is adjustable, the circle-radius being lso dj s l The p e ious y known modified impedance relays have required ,a separate element for each phase, In one of the forms of embediment of this modified impedance relay,

which ha be f un wh t's rery desi a le rt sponse-char acteristics an instantaneous ba l:- aneed beam relay is used, haying its operating ide iust bly en r i ed in respo se o t e linecurrent an h ving its re tr intide e g zed in response to an E+ quant ty hich is ttoriall compounded of a resp nse to the nevolta p us a variable-m ni de e ponse to the lin -c rr nt, displaced 90; and adj ta le in p se-an le with respe t to said 90 d sp a ment,-

An object of my Present invention is to :prode t o networ s ,fo s le t g the mete phas quan ties to b a p d t a s n le modifi d mpedance element, so that a sin le element will suflice for all three phases of the protected threephase line. n h op ra ing side of t e la the line-current which flows in the faulted phase will be larger than either of the other two line cnrrents, so that the proper-phase can be selected by a maximum-current network such as that which is described in the'HarderPaten-t No. 2,242,950 of 1941. On the restraint-side of the relay, which receives an (E +1) quantity, the magnitude of the I component does not need to be very large, and I have found that this (E-l-I) quantity is generally the least on the faulted phase, so that the proper phase can be selected by means of aminvimum-voltage network, a preferred form of which is shown in my copending application serial No. 788,583, filed November 28, 1947, now Patent No. 2,504,827, issued April 18, 1950. Both the maximum-voltage network and the minimumevoltage network use rectifiers, so that my singleaelement mo ifi d impedance relayas dire tkturrent energization.

' W th the oregoing and oth r objec s in i w. my in entio co sis s of he r iuits, sys ms, omb nati ns, ap atus ts, and method of design and. bpfiiation described and claimed in he ol ow specifica io a d llus rat d n t e ac panyin drawing the s gle ure f which s a simpl fied diae amm ie Vi w of rcuits and appa tus embedy ne in ntion an l u tra lte te m of embod m n I l ustra ed my nvel tion as b ng appl ed to th pr e ti n o a lin -section 1', whi h may e a pa t o a threehase s styr e ran iss on or di tribut n s stem- The t e-phase l is e timate to a hr e-ph e bu 2 through ne=sesrssatin tirtuit-interrtlpt ns me n 3, which is to be eontrolled hys itahle iatilt-respone site Rh me-mean The i lustrat d m of e bo ment of my itmention uses Dhase-to-phas lineecurrents, which are deriyed hy means of a bank of delta-connected in cu rent ransfe me s 4 T eil u tm d Y m also us s swe ts-the e cl n aees whiq are dented rem a t o Pot nti l -t ansfo mer A, 55 and 593 one fo ach of the ii e phase A B and C,-

moiified mp dente t ayis an i tantan ous balanced-beam relay MZ, shown at the botome: the drawing, and haying relayecontaets 6 which a e at di my 91 a -.m, mb.er .ot orms s t ip rsm y tems not sh wn), for ontrol ng e ti c i eint r l pt 3 in r ns to rhaseefau t on the pmtett d tlin esett on J The relay M2 i differentially sponsive to the fumes exer d by n operatine side el ctrom gsme 1 and arestraint-side electromagnetam i As vs wn in any rev ous y ment oned patents on he i d -i I 1 e a lce rela t e pe at n de of the e ay :is e er ed by means o n adly ta p d wa ting 9. .1 9 wh h is d stably respons ve t9 the magnitude f th line-ou e in the-tainted phase, wcco anse wi h m present invention, this on ating -coi1 9 is enerze by a maX mumr tage PrV- E wh eh consists of three rect fierabri ges H which are imp es ed di i r nt alternatingecurrent -Volt ge which are obtai ed :by assin the l ne-cirrrents, in :the respective line-phases throngh reistors r imp d nees as, andZQ-resnw vely, oneior each phase, The direeteenrrent outputterrninals of ,the three bridges H are 00 e her para lel, to a ommon o tp" '2, Which t ils has a voltage e0 es on he larg st one of the impressed a ternating-eurrent input voltages of the network. These output-terminals I2 are used to energize the operating-coil 9 of the modified impedance relay MZ. If desired, the output-terminals i2 can be shunted by a ripple-suppressing capacitor 13. The principles of this maximum-voltage network Emax are further explained in the previously mentioned Harder patent.

In accordance with my invention, the restraintmagnet 8 of the modified impedance relay M2 is energized in accordance with the minimum one of three (E+I) quantities, as selected by a minimum-voltage network Emin. The type of minimum-voltage network Emin which has been selected for illustration in the drawing is one of the forms of network which is disclosed in my previously mentioned copending application. It comprises three rectifier-bridges 14 which are respectively energized by means of three different (E+I) quantities, one for each phase.

The positive terminals I5 of the three bridges M of the minimum-voltage network Emin are all connected together, and to a common positive bus which represents the positive terminal of an auxiliary direct-current source, such as a station-battery, the negative terminal of which is indicated at The negative terminals of the three bridges [4 are indicated at [6A, [6B and ISO respectively, and these are connected, through individual rectifiers RA, RB and RC respectively, to a common negative bus I! which is used to energize one terminal of a restraining winding [8 on the restraint-magnet frame 8, the other terminal of the restraining winding l8 being connected to the negative source-terminal The three rectifiers RA, RB and RC conduct current in the direction toward the common negative bus IT. The direct-current output-terminals of the several bridges I4 are shunted by individual shunting-resistors I9, each of which is preferably shunted, also, by means of a ripple-suppressing capacitor 20. The minimum-voltage network Emin also uses an operating winding 2| which is also mounted upon the restraint-magnet frame 8, and which is directly energized across the positive and negative terminals and of the auxiliary direct-current source, in such polarity as to oppose the ampere-turns of the restraintcoil l8.

The three (E+I) quantities which are used to energize the rectifier-bridges 14 of the minimumvoltage network Emln are compounded of a voltage response which is obtained from the appropriate potential-transformer 5A, 5B or 50, as the case may be, plus a current-response which is preferably obtained, as shown in the illustrated form of embodiment of my invention, by means of an auxiliary air-gap current-transformer or mutual reactance yM, one for eachphase. Each of these mutual reactances giM has an adjustably tapped primary winding 23, which is energized from its corresponding phase of the line-current transformers 4. Each mutual reactance y'M also has a secondary winding 24 which is connected in series with the voltage-leads of the corresponding phase of the potential-transformers 5A, 5B or 5C, as the case may be. The phase of the current-component which is thus introduced in series with the line-voltage response is adjustable by any suitable means, a simple, and usually adequate, phase-adjustment means being illustrated in the form of a variable resistor 25 which is shunted across a portion of the secondary winding 24 of each of the mutual reactances :iM.

In the operation of my device, the maximumvoltage network Emax selects the largest voltage which is produced by the passage of the various line-currents through the several resistances or impedances ZA, ZB and ZC, respectively. This impresses, on the direct-current output-terminals l2 of the three rectifier-bridges II, a voltage corresponding to the magnitude of the rectified voltage of the largest'input-phase. Assuming that the rectifier-bridges ll of the two other inputphases do not conduct any current in the nonconducting direction, and assuming that these two other input-phases have voltages which are smaller, in magnitude, than the largest phase, then no current can flow in these two bridges ll corresponding to said two smaller phases, and thus the largest phase is selected by the network. This applies, to the operating magnet 1 of the relay MZ, a voltage corresponding, in magnitude, to the largest of the three line-currents, and hence corresponding to the current in the faulted phase.

The minimum-voltage network Emln responds, as follows, to the smallest of the three voltages which are impressed upon the rectifier-bridges 14. Assuming, for example, a phase-A fault, it will be obvious that the phase-A line-voltage will be the smallest of the three line-voltages, and I have found that, in general, the (E+I) quantity, in this phase, will also be the smallest of the three (E+I) quantities, particularly when the magnitude of the currentcom'ponent which is vectorially added to the voltage-component is not too large, and considering the fact that this currentcomponent is dephased with respect to the voltage-component.

Assuming a phase-A fault, therefore, the output of the phase-A rectifier-bridge ll of the minimum-voltage network Emin will impress the rectified phase-A (E+I) voltage across the terminals of the corresponding loading-resistor l9, so that the restraint-coil 18 will be impressed with a voltage equal to the voltage E of the auxiliary source having the terminals and minus the rectified phase-A (E+I) voltage, the energizingcurrent for this restraint-coil l8 being supplied by means of the phase-A rectifier RA. Assuming that the other two rectifiers RB and RC do not carry any current in their reverse-current direction, and assuming that the impressed voltages on the phase-B and phase-C bridges M are smaller than the voltage impressed upon the phase-A bridge hi, it will be evident that the negative bridge-terminals IBB and IE0 will be more negative than the common negative bus H, but no current can flow thereto from said common negative bus IT, by reason of the rectifiers RB and RC, thus causing the restraint-coil 18 to be impressed with the difference between the source-voltage E and the rectified voltage of the minimum (E+I) quantity. The energization of the operating coil 2| on the restraint-magnet 8 of the relay MZ is responsive to the source-voltage E, and of such magnitude as to cancel the E part of the energization of the restraint-coil l8, leaving a response solely to the smallest of the three (E+I) quantities of the line.

The modified impedance relay MZ, as explained in my previously mentioned patents, particularly Patent No. 2,393,983, has a characteristic response-circle which is triply adjustable, the circle-radius being adjustable by adjusting the strength of the energization of the operating-coil 9, as by adjusting the taps thereon, while the amount of center-displacement of the circle with respect to the origin of the rectangular coordinates is determined by the tap-adjustment on the primary windings 23 of the three mutual reactors 7M, and the angle of the line in which the circlecenter is displaced is determined by the adjustment of the phase-adjusting means 25.

It will be understood, of course, that my present invention would be used as a part of a much larger, more complex relaying system, with provisions for ground-fault protection, and usually also various forms of back-up protection, with supervision in response to the direction of the line-current, and sometimes also carrier-current supervision, none of which details are shown in the drawing. It will also be understood that the example which I have given is only illustrative. I could have used other means for deriving the (E+I) quantities, other forms of maximum or minimum-voltage networks, other types of reactance relays, and the like, although the illustrated example has considerable merit. I wish it to be understood, therefore, that my invention, in its broadest aspects, is subject to considerable modification, in the way of additions, omissions, and the substitution of equivalents, and I desire that the appended claims be given the broadest interpretation consistent with their language.

I claim as my invention:

1. A single-element relay for a polyphase line, said relay having two energizing-means for producing two relay-fluxes, a maximum-voltage network for energizing one of said energizing-means, and a minimum-voltage network for energizing the other of said energizing-means, said maximum-voltage network having a plurality of alternating-current input-circuits and a plurality of rectifier-means for energizing common directcurrent output-circuit in accordance with the largest of the input-voltages, means for energizing the respective input-circuits of the maximumvoltage network in accordance with the voltagedrops across a plurality of impedances traversed by difierent line-currents of the polyphase line, said minimum-voltage network having a plurality of input-circuits and a plurality of rectifiermeans for energizing a common direct-current flux-producing means in accordance with the smallest of the input-voltages, and means for energizing the respective input-circuits of the minimum-voltage network in accordance with the vectorial sums of difierent (E+I) quantities, in difierent phases of the polyphase line, where E and I are relatively dephased line-voltages and line-currents, respectively, the line-current responses I being sufiiciently small so that the (E-i-I) quantity in the faulted phase is in general the smallest of the plurality of (E +1) quantitles.

2. The invention as defined in claim 1, characterized by said relay being differential relay having an operating means which is responsive to the output of the maximum-voltage network, and having a restraining means which is respon-' sive to the output of the minimum-voltage network.

SHIRLEY L. GOLDSBOROUGH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,393,043 Harder Jan. 15, 1946 2,393,983 Goldsborough Feb. 5, 1946 2,426,062 Sonnemonn Aug. 19, 1947 2,479,345 Goldsborough Aug. 16, 1949 FOREIGN PATENTS Number Country Date 589,153 Germany Dec. 4, 1933 

